1. Field of the Invention
The present invention generally relates to data defect detection using soft decision result, and more particularly to a defect detection device for a data reproduction apparatus such as an optical disk unit or a magnetic disk unit, the defect detection device detecting a defect of recorded data based on a reproduced signal from a recording medium and a data reproduction apparatus including the same. The present invention also relates more particularly to a data defect detection method based on a reproduced signal from a recording medium and a data reproduction method based on such a data defect detection method.
2. Description of the Related Art
Recently, as information is recorded on a recording medium such as a magneto-optical disk at a higher density, more efforts have been made to increase a data transfer rate in the reproduction system of the magneto-optical disk. As a method of performing high-speed information reproduction with high accuracy from such a magneto-optical disk recorded with information at high density, a recording and reproduction method according to PRML (Partial Response Maximum Likelihood) is proposed.
According to this PRML recording and reproduction method, a magneto-optical disk is recorded with a signal with a partial response (PR) waveform, and a reproduced signal from the magneto-optical disk is sampled in synchronism with a predetermined clock signal so as to obtain sampled values. Data having maximum likelihood is reproduced from the sampled values (quantized data) in accordance with a maximum likelihood (ML) algorithm such as the Viterbi decoding algorithm.
With respect to a data reproduction apparatus based on the above-described PRML recording and reproduction method, such as a magneto-optical disk unit, it is proposed to detect a variation in the direct current level of the reproduced signal and feed back the variation level to information for data demodulation, such as expected values or sampled values employed for maximum likelihood decoding. Thereby, data is reproducible with high accuracy from sampled values of a reproduced signal even if the reproduced signal varies in its direct current level.
In such a data reproduction apparatus as described above, if recorded data includes a defect resulting from a physical defect of a recording medium, such as a flaw or adhesion of dust, or from a defective operation in writing the data to the recording medium, the data is prevented from being properly reproduced from sampled values of a reproduced signal affected by such a defect. Therefore, it is important to detect such a defect of the recorded data.
Further, in a data reproduction apparatus in which the level variation of a reproduced signal is fed back to information used for data demodulation, it becomes an issue how to control the feedback of the variation level to the information for data demodulation in a defect-containing part and the other normal part of recorded data.